Prevent a non-root user from shutting down or rebooting the system

To prevent all non-root users from using the shutdown, reboot or halt commands, do the following :

1. In the file /etc/X11/gdm/gdm.conf , change the line that reads :
   

   SystemMenu=true

   to
   

   SystemMenu=false

2. In the file /etc/inittab, change the line that reads :
   

   ca:ctrlaltdel:/sbin/shutdown -t3 -r now

   to
   

   ca:ctrlaltdel:echo "You are not authorized to turn off the machine"

3. In the directory /etc/security/console.apps/, delete the file reboot, poweroff and halt.
4. Remove the file /usr/bin/poweroff

Now only the root user will be able to turn off or reboot the machine.